There are very few of those for sale anywhere in the U.S. It will stick out like a sore thumb if they advertise it anywhere. You should contact Global Equipment Exporters in Acworth,Ga. They are one of the few dealers that typically have used stumpgrinders like this for sale. The thief might try to sell it to them. There is a large tree service forum where these big grinders show up for sale now and then. I don't know if I can mention it here, but will try.
It is called "arboristsite" It would be a great place to post about this loss. Also, use one of the search programs to search Craigslist nationwide every day or so.
I hope you get it back and the police get the nogoods who took it.